PROJECT SUMMARY Acetylcholine (ACh) is an important neurotransmitter involved in attention, arousal, visual processing, motor control, and motivated behavior. Cholinergic transmission is perturbed in a number of devastating human disorders/diseases, including Alzheimer's disease, Parkinson's disease, major depression, and drug addiction. Muscarinic ACh receptors are GPCRs, whereas nicotinic ACh receptors (nAChRs; the subject of this proposal) are a family of Cys-loop, ligand-gated cation channels. nAChRs exist either as homopentamers containing 5 a7 subunits, or heteropentamers requiring 2 a subunits, 2 b subunits, and a 5th subunit that may be either an a or a b subunit. Studies aimed at probing nAChR function in the vertebrate brain have relied principally on rodent studies, where mouse genetic techniques have permitted key insights. A key gap in the field is the lack of suitable tools for nAChR gene editing. This R21 project will fill that gap via two independent scientific aims. In Aim 1, we will create ? for each key nAChR subunit gene ? a single vector that will catalyze CRISPR-mediated gene editing that results in a loss-of-function mutation. Guide RNA species will be validated in vitro prior to vector construction. Vectors will be further validated in vivo via gene expression analysis and patch clamp electrophysiology. This set of vectors will be useful for brain-region specific nAChR gene editing in any recipient mouse strain, including selectively-bred strains whose genetics cannot be disturbed by crosses to C57BL/6 or other common backgrounds. In Aim 2, we will create a parallel series of vectors to allow for cell type-specific nAChR gene editing. Vetted gRNAs from Aim 1 will be incorporated into a set of vectors that will be introduced into a specialized set of mouse strains that produce Cas9 nuclease in a Cre-dependent manner. As in Aim 1, we will validate this system in vivo using gene expression analyses and patch clamp electrophysiology. Ultimately, these new vectors will greatly expand our molecular toolbox, allowing for wide control over nAChR gene editing in various genetic backgrounds and in specific circuits.